A. Technical Field
The present invention relates to a detergent builder, a production process therefor, and a poly(meth)acrylic acid (or salt) polymer and a use thereof.
B. Background Art
The poly(meth)acrylic acid (or salt) polymer is a useful polymer and, for example, used for detergent builders, scale inhibitors, and inorganic pigment dispersants. A typical production process therefor comprises the step of polymerizing a monomer component including a major proportion of (meth)acrylic acid (or salt) in the presence of a chain transfer agent and a polymerization initiator in an aqueous medium.
U.S. Pat. No. 2,789,099 discloses a production process for a polyacrylic acid polymer comprising the step of carrying out a polymerization reaction of an aqueous solution containing acrylic acid, a peroxide (as a polymerization initiator), and a specific copper compound and a specific alkaline-metal hypophosphite (as chain transfer agents), and sets forth an example of preferred embodiments (working example) in which raw materials are charged all at once and then heated to carry out polymerization, and further, another example in which raw materials other than the peroxide are initially charged and heated, and thereafter, the peroxide is added, while the polymerization is carried out. This prior USP exemplifies fiber-sizing agents, soil stabilizers, adhesives, and emulsifiers as uses of the polyacrylic acid polymer.
JP-A-011092/1980 discloses the use of a specific poly(meth)acrylic acid polymer (telomer compound) as an aqueous treating agent, and sets forth an example of preferred embodiments (working example) in which the telomer compound is produced by a process comprising the step of dropping an aqueous sodium persulfate solution and acrylic acid to an aqueous sodium hypophosphite solution and heating the resultant mixture.
JP-A-293599/1986 relates to a heat-resistant scale inhibitor comprising a poly(meth)acrylic acid polymer, and sets forth an example of preferred embodiments (working example) in which water is charged into a reactor and then heated, and thereafter, an aqueous acrylic acid solution, an aqueous hypophosphorous acid (or salt) solution, and an aqueous polymerization initiator solution are dropped thereto, while the polymerization is carried out, and further, another example in which a hypophosphorous acid solution is charged into a reactor and then heated, and thereafter, acrylic acid (aqueous solution) and a polymerization initiator (aqueous solution) are dropped thereto, while the polymerization is carried out.
The gelation resistance and the chelating ability are exemplified as main properties as demanded when the poly(meth)acrylic acid (or salt) polymer is, for example, used for detergent builders, inorganic pigment dispersants, and scale inhibitors. The gelation resistance is an index showing the unlikeliness of the occurrence of a phenomenon in which polycharged metal ions, such as calcium ion, present in the system, precipitates and gels due to contact with the poly(meth)acrylic acid (or salt) polymer, and it is generally assumed that the higher the molecular weight is, the lower the gelation resistance is. On the other hand, the chelating ability is an index showing the ability to chelate the polycharged metal ions, such as calcium ion, present in the system, and it is generally assumed that the higher the molecular weight is, the better the chelating ability is. Thus, there is a trade-off relation between the gelation resistance and the chelating ability with regard to the molecular weight, so it is difficult to obtain good results with regard to both the gelation resistance and the chelating ability.
Furthermore, any of the poly(meth)acrylic acids (or salts), as obtained by the processes as disclosed in the above prior art documents, has so broad a molecular weight distribution that high-molecular and low-molecular components, greatly deviating from the average molecular weight, are present, and these components are the causes to lower the gelation resistance and the chelating ability respectively.